1. Field of the Invention
This invention relates to a chipping apparatus for materials and a disk-shaped chipping element.
2. Description of the Background Art
Conventional chipping devices in this class are known, for example, as disk mills, refiners, beater mills, or cone mills. In these chipping devices, the dumpable material is fed axially into the center of the chipping chamber, which is enclosed by the housing, and is then diverted into a radial direction, where chipping tools rotating around a central axis of rotation take hold of and chip the material.
The chipping tools are located inside the housing relative to one another at an axial or radial distance, and thus form a rotation-symmetrical milling gap where the chipping process takes place. The material is hurled against the profiled surface of the chipping tools, where it is broken up and crushed. For this purpose, the chipping tools are equipped with a specially designed surface, which, for the most part, is formed of riffle strips that are arranged radially.
During the operation of the conventional chipping apparatus, the riffle strips are exposed to heavy mechanical wear and tear, which, among other factors, is influenced by the type and purity of the material to be chipped. This results in natural wear of the chipping tools so that the worn-down chipping tools have to be replaced at regular time intervals. Customarily, the chipping tools are either replaced or recycled, by reconditioning the riffle strips through filing and sharpening. However, each time reconditioning takes place the thickness of the chipping tools decreases. Thus, reconditioning cannot be repeated interminably, rather, for static reasons, it must stop when the gradual weakening of the chipping tool cross-section has progressed to a point where the chipping tools are no longer able to withstand the mechanical stress during the chipping process.
This borderline divides a chipping tool, over its thickness, into a core area and a utilization area. The utilization area, on the surface of which the chipping process takes place, is characterized in that, through progressing wear and tear, it can be completely used up without risk to the function and fracture safety of the chipping tools. Thus, it is possible to completely use up the utilization area of the chipping tools when regrinding them.
The core area, on the other hand, is the part of the chipping tool, which is necessary for static reasons, so that the chipping tools do not break during the operation of a chipping apparatus. Therefore, the danger of using a chipping tool beyond its utilization area is that the chipping tool can no longer withstand the heavy mechanical stress and will be destroyed. The fragments resulting therefrom can lead to serious damage to the entire chipping apparatus.
A way to determine the state of attrition of the chipping tools, that is, to determine if the thickness of the chipping tool is sufficient from a static standpoint, is to check the remaining thickness of the chipping tool with the aid of gauges. This is done manually using an appropriate tool, whereby a measurement can only be taken at an edge of a chipping tool. This way of determining the state of attrition is relatively labor intensive, so that in the work place this procedure is often not done at all or not often enough. Moreover, the disadvantage of this procedure is that there is no automatic indicator of the state of attrition, that is, the operator of such a chipping apparatus has to check the state of attrition on his/her own initiative.
Another way to indicate the state of attrition of chipping tools is to put markings on the sides of a chipping tool that make up the thickness. These markings are in the division line between the utilization area and the core area. When the utilization area is reduced to where the marking is, the chipping tool must be replaced with a new one. The disadvantage of markings is that if put on the surface of the chipping tool, they can be erased by mechanical use and thus become invisible. When using stamps there is the danger that dirt deposits, which accumulate in the stamps over time, will make them hard to recognize.
Both procedures have the disadvantage that an examination of the state of the chipping tools can only take place at their edges. With uneven wear and tear, getting below the static minimum thickness in the middle of the surface remains undetected.